Frog blastula nuclei transplanted into first meiotic metaphase oocytes respond to the meiotic events, and when the oocytes are matured and activated, the somatic nuclei transform into "fertilization" nuclei and promote embryogenesis. Non-cycling erythrocyte nuclei from terminally differentiated cells also respond to meiotic events and after activation of matured oocytes, they are induced to synthesize DNA.